######## WORK NOTES COPIED FROM INCIDENT 393941 ########
**** Entered By: clsalvin @ 04/11/2005 05:18 PM ****
QUESTION 1:
Using the stacking factor approach proposed in the Ansys LF EMAG Training Manual, Release 8, Pg 227,
there is a model for mu_rx, and mur_y. I plotted these as a function
of the stacking factor, and the resulting plot is attached as the file
'StackingFactor.bmp'.
Looking at this file, I see that in the ydirection the mu_r is extremely
small. I am wondering if this is expected? It should mean that the
attraction
force would be extremely small, if an axiallymagnetized magnet was
placed UNDERNEATH the stack shown on Page 227. But our general
observation suggests otherwise!
ANSWER 1:
This variation in the inplane and normal relative permeability versus stacking factor (your plot) is exactly what I would expect. The stacking factor is useful for calculating the overall FIELD, but I can see how FORCES may not be correctly calculated for the normal (y) direction because PHYSICALLY, the flux from the PM will impinge the first iron lamination which has the full value of mu_r. The "smeared properties" modeling approach will in effect present the impinging flux with a much lower mu_iron/mu_air ratio and so calculated forces could be significantly lower than expected (since force increases with difference in permeability at the material interface).
If force is important to you, I would model individual laminations near the surface and transition to a "smeared properties" mesh below the laminations to reduce element count.
QUESTION 2:
I want to model different nonlinear permeability acting in different directions in a 3D model. I see in your documentation that one may only define a single BH curve for any given material, with optional linear permeabilities superceding the BH curve in specified directions. Is there a workaround allowing definition of different BH curves actingin different directions?
ANSWER 2:
I do not h
######## WORK NOTES COPIED FROM INCIDENT 393941 ######## **** Entered By: clsalvin @ 04/11/2005 05:18 PM **** QUESTION 1: Using the stacking factor approach proposed in the Ansys LF EMAG Training Manual, Release 8, Pg 227, there is a model for mu_rx, and mur_y. I plotted these as a function of the stacking factor, and the resulting plot is attached as the file 'StackingFactor.bmp'. Looking at this file, I see that in the ydirection the mu_r is extremely small. I am wondering if this is expected? It should mean that the attraction force would be extremely small, if an axiallymagnetized magnet was placed UNDERNEATH the stack shown on Page 227. But our general observation suggests otherwise! ANSWER 1: This variation in the inplane and normal relative permeability versus stacking factor (your plot) is exactly what I would expect. The stacking factor is useful for calculating the overall FIELD, but I can see how FORCES may not be correctly calculated for the normal (y) direction because PHYSICALLY, the flux from the PM will impinge the first iron lamination which has the full value of mu_r. The "smeared properties" modeling approach will in effect present the impinging flux with a much lower mu_iron/mu_air ratio and so calculated forces could be significantly lower than expected (since force increases with difference in permeability at the material interface). If force is important to you, I would model individual laminations near the surface and transition to a "smeared properties" mesh below the laminations to reduce element count. QUESTION 2: I want to model different nonlinear permeability acting in different directions in a 3D model. I see in your documentation that one may only define a single BH curve for any given material, with optional linear permeabilities superceding the BH curve in specified directions. Is there a workaround allowing definition of different BH curves actingin different directions? ANSWER 2: I do not have much experience modeling orthotropic properties/lamination stacks in 3D, however I did once devise a strategy for modeling 2 separate BH curves in one region in 2D (see attached zip file). You should be able to extend this to 3D if you need to.I expect this method may suffer the same loss of accuracy for force calculations since it "smears" properties of a lamination stack and so fails to model the full ratio of permeability that flux impinging the surface encounters. So, as I mentioned earlier, I would model individual laminations near the surface and transition to a "smeared properties" mesh below the laminations to reduce element count. 

